As it explains: by achieving parity with wingdings, dependence on (generally copyrighted) wingding fonts can be removed. This also has the side benefit of improving usability because now your cute glyph isn't pronounced "m" by the text to speech but as what it actually depicts.

Also, as far as i can understand, this doesn't remove dependency on fonts, as its only codepoints definitions, somebody still has to do the font (and, as i can imagine, most font authors wont give a damn about most symbols anyways).

You should visit some tackier, less tasteful websites! Or maybe you just don't have wingdings and webdings.

The point is that they're in the unicode standard so they can be in standard fonts and not an arbitrary Microsoft extension.

Edit, to expand on this point: of course the "levitating man" glyph is silly but he serves our purposes well:

A webpage can say they need the letter "m" and it MUST BE WINGDINGS or bust,

Or it can say it needs the levitating man, and the browser/OS can peruse its list of fonts to find the highest preference one which provides the symbol by that name, regardless of whether it's wingdings.ttf.